The present invention relates generally to an improvement in the measurement of color registration in an electronic reprographic printing machine, and more particularly to a test pattern generated within the electronic reprographic printing machine that enables a field technician to quickly and efficiently verify color registration.
The marking engine of an electronic reprographic printing system is frequently an electrophotographic printing machine. In an electrophotographic printing machine, a photoconductive member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter selectively exposed. Exposure of the charged photoconductive member dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image on the photoconductive member is developed with charged toner which is subsequently transferred to a copy sheet. The copy sheet is heated to permanently affix the toner image thereto in image configuration.
Multi-color electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complementary thereto. This process is repeated a plurality of cycles for differently colored images and their respective complementarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multi-layered toner image on the copy sheet. Thereafter, the multi-layered toner image is permanently affixed to the copy sheet creating a color copy. The developer material may be a liquid or a powder material.
In the process of black and white printing, the copy sheet is advanced from an input tray to a path internal to the electrophotographic printing machine where a toner image is transferred thereto and then to an output catch tray for subsequent removal therefrom by the machine operator. In the process of multi-color printing, the copy sheet moves from an input tray through a recirculating path internal to the printing machine where a plurality of toner images is transferred thereto and then to an output catch tray for subsequent removal. With regard to multi-color printing, a sheet gripper secured to a transport receives the copy sheet and transports it in a recirculating path enabling the plurality of different color images to be transferred thereto. The sheet gripper grips one edge of the copy sheet and moves the sheet in a recirculating path so that accurate multi-pass color registration is achieved. In this way, magenta, cyan, yellow, and black toner images are transferred to the copy sheet in registration with one another.
The quality of the final color copy or printed sheet of a multi-color electrophotographic printing system depends on the alignment of the magenta, cyan, yellow, and black images on the sheet of paper during a toner transfer stage. Color registration is a term well known in the art that refers to the level of alignment between several images. A typical color registration error is 125 microns. In other words, to have proper color registration each of the four images cannot be misaligned more than 125 microns from any other color.
The sophisticated equipment to accurately test the color registration of a color copier or printer is both large and expensive. This equipment has the capability of measuring the color registration error at any location on an image and in which direction a given color image is skewed. When testing color copiers and printers, it is typically impractical to have field technicians bring such equipment to each and every site.
Therefore, there is a need for a method and apparatus that is quick and inexpensive to measure the color registration error of a color copier or printer.
There is also a need for a method and apparatus that determines the direction of the color registration error for a given color image.
Furthermore, there is a need for a method and apparatus that determines the color registration error at any location on the image.